Ni based alloy with excellent corrosion resistance to supercritical water environments containing inorganic acids

ABSTRACT

A Ni based alloy with a composition including Cr: from more than 43% to 50% or less, Mo: 0.1% to 2%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.05% to 0.5%, and where necessary also including either one, or both, of Fe: 0.05% to 1.0% and Si: 0.01% to 0.1%, and the remainder as Ni and unavoidable impurities, in which the quantity of C amongst the unavoidable impurities is restricted to 0.05% or less. It has excellent corrosion resistance relative to supercritical water environments containing inorganic acids. Also provided is a member for a supercritical water process reaction apparatus comprises the Ni based alloy.

CROSS-REFERENCE TO PRIOR APPLICATION

This is a U.S. national phase application under 35 U.S.C. § 371 ofInternational Patent Application No. PCT/JP03/00075 filed Jan. 8, 2003,and claims the benefit of Japanese Patent Application Nos. 2002-1217filed Jan. 8, 2002; 2002-1218 filed Jan. 8, 2002; 2002-232838 filed Aug.9, 2002 and 2002-232847 filed Aug. 9, 2002 which are incorporated byreference herein. The International Application was published inJapanese on Jul. 17, 2003 as WO 03/057933 A1 under PCT Article 21(2).

TECHNICAL FIELD

The present invention relates to a Ni based alloy with excellentcorrosion resistance to (i) supercritical water containing inorganicacids such as hydrochloric acid, sulfuric acid, phosphoric acid andhydrofluoric acid generated by the decomposition and oxidation oforganic toxic materials such as VX gas, GB (sarin) gas and mustard gasused in chemical weapons and the like, or (ii) supercritical watercontaining inorganic acids such as hydrochloric acid generated by thedecomposition and oxidation of organic toxic materials such as PCBs anddioxin, which represent industrial waste products for which disposal isdifficult. The invention also relates to a member for a supercriticalwater process reaction apparatus formed from such a Ni based alloy.

Furthermore, the present invention also relates to a Ni based alloy thatdisplays excellent resistance to stress corrosion cracking insupercritical water environments containing inorganic acids, and amember for a supercritical water process reaction apparatus formed fromsuch a Ni based alloy, and more particularly to a Ni based alloy thatdisplays excellent resistance to stress corrosion cracking in (i)supercritical water environments containing non-chlorine based inorganicacids such as sulfuric acid, phosphoric acid and hydrofluoric acidgenerated by the decomposition and oxidation of organic toxic materialssuch as VX gas, GB (sarin) gas and mustard gas used in chemical weaponsand the like, or (ii) supercritical water environments containinginorganic acids that comprise chlorine such as hydrochloric acidgenerated by the decomposition and oxidation of organic toxic materialssuch as PCBs and dioxin, which represent industrial waste products forwhich disposal is difficult, as well as a member for a supercriticalwater process reaction apparatus formed from such a Ni based alloy.

BACKGROUND ART

Water at a temperature/pressure exceeding the critical point(specifically, water at a temperature/pressure exceeding 374° C./22.1MPa) is known as supercritical water, and is capable of dissolving ahuge variety of materials. Water in this supercritical state exists in anon-condensable, high density gaseous state, and is capable ofcompletely dissolving non-polar or very slightly polar materials (suchas hydrocarbon compounds or gases) which display only very limitedsolubility in water at room temperature, and it is reported that by alsoadding oxygen to the supercritical water, these dissolved materials canbe oxidized and decomposed.

The organic toxic materials used in chemical weapons and the like are noexception, and can be dissolved completely in supercritical water, andby also incorporating dissolved oxygen in the supercritical water andreacting the organic toxic materials contained within the chemicalweapons or the like in the supercritical water, oxidation anddecomposition into non-toxic materials such as carbon dioxide, water,sulfuric acid and phosphoric acid can be achieved. For example, VX gascan be oxidized and decomposed into sulfuric acid and phosphoric acid,and GB gas can be oxidized and decomposed into hydrofluoric acid andphosphoric acid. Accordingly, in recent years in the U.S.A., tests havebeen conducted on using supercritical water in the disposal of chemicalweapons that contain VX gas, GB (sarin) gas, mustard gas or the like, bydecomposing and oxidizing, and thus detoxifying, the organic toxicmaterials of VX gas, GB (sarin) gas and mustard gas, which are difficultto break down under normal conditions. Once this method for decomposing,oxidizing and detoxifying the organic toxic materials of VX gas, GB(sarin) gas and mustard gas and the like using supercritical waterbecomes established, it will provide a much more environmentallyfriendly process than the conventional incineration treatment methods,as the supercritical water and oxidizing agent have no adverse effectson the environmental. Furthermore, because supercritical water is highlyreactive, organic toxic materials such as VX gas, GB (sarin) gas andmustard gas can be decomposed, oxidized and detoxified within a shortperiod of time. In addition, the decomposition treatment can be carriedout within a closed system, meaning there is no danger of environmentalpollution caused by emissions or discharge.

Furthermore, organic toxic materials such as PCBs and dioxin, whichrepresent industrial waste products for which disposal is difficult, arealso no exception, and can be dissolved completely in supercriticalwater. By adding oxygen and reacting the organic toxic materials withinthe supercritical water, oxidation and decomposition into non-toxicmaterials such as carbon dioxide, water, and hydrochloric acid can beachieved. This process can be carried out within a closed system,meaning that compared with conventional incineration treatment methods,there is no danger of environmental pollution caused by emissions ordischarge.

When supercritical water is used as the reaction solvent for decomposingand oxidizing organic toxic materials such as VX gas, GB (sarin) gas andmustard gas, the oxidation and decomposition in high temperature, highpressure (400° C. to 650° C., 22.1 MPa to 80 MPa) supercritical watergenerates a mixture of inorganic acids such as sulfuric acid andphosphoric acid with a high concentration of oxygen. As a result, inorder to enable supercritical water to be used as the reaction solventfor decomposing, oxidizing, and detoxifying organic toxic materials suchas VX gas, GB (sarin) gas and mustard gas, the process reactionapparatus in the system used for detoxifying these organic toxicmaterials, and in particular the material used for producing the processreaction vessel, must display good corrosion resistance relative to thistype of supercritical water environment containing inorganic acids.

Furthermore, when supercritical water is used as the reaction solventfor decomposing and oxidizing organic toxic materials such as PCBs anddioxin, the oxidation and decomposition in high temperature, highpressure (400° C. to 650° C., 22.1 MPa to 80 MPa) supercritical watergenerates a mixture of inorganic acids containing chlorine such ashydrochloric acid together with a high concentration of oxygen. As aresult, in order to enable supercritical water to be used as thereaction solvent for decomposing, oxidizing, and detoxifying organictoxic materials such as PCBs and dioxin, the material used for producingthe process reaction vessel in the system used for detoxifying theseorganic toxic materials must display good corrosion resistance relativeto this type of supercritical water environment containing inorganicacids.

Consequently, Ni based corrosion resistant alloys, which are widelyknown as being highly resistant to corrosion, have been proposed as onepossibility for a metal material that could be used for the processreaction apparatus used with supercritical water. Specific examples ofsuch Ni based corrosion resistant alloys include Inconel (a registeredtrademark) 625 (as prescribed in ASTM UNS N06625, with a composition,expressed as weight percentages, that comprises, for example, Cr: 21.0%,Mo: 8.4%, Nb+Ta: 3.6%, Fe: 3.8%, Co: 0.6%, Ti: 0.2%, and Mn: 0.2%, withthe remainder being Ni and unavoidable impurities), and Hastelloy (aregistered trademark) C-276 (as prescribed in ASTM UNS N10276, with acomposition that comprises, for example, Cr: 15.5%, Mo: 16.1%, W: 3.7%,Fe: 5.7%, Co: 0.5%, and Mn: 0.5%, with the remainder being Ni andunavoidable impurities). Recent reports have stated that Ni based alloyswith even higher Cr contents display even better corrosion resistancerelative to supercritical water containing inorganic acids. As a result,high Cr content Ni alloys such as MC alloy (with a compositioncomprising Cr: 44.1%, Mo: 1.0%, Mn: 0.2%, and Fe: 0.1%, with theremainder being Ni and unavoidable impurities) and Hastelloy G-30 (asprescribed in ASTM UNS N06030, with a composition that comprises, forexample, Cr: 28.7%, Mo: 5.0%, Mn: 1.1%, Fe: 14.6%, Cu: 1.8%, W: 2.6%,and Co: 1.87%, with the remainder being Ni and unavoidable impurities)are now attracting considerable attention as potential materials forreaction apparatus.

However, amongst conventional Ni based alloys, Inconel 625 and HastelloyC-276 do not provide adequate corrosion resistance to supercriticalwater containing acids such as sulfuric acid, phosphoric acid andhydrofluoric acid, and consequently if either of these materials isemployed in a process reaction apparatus in a system used fordetoxifying organic toxic materials, particularly if employed as thematerial for producing the process reaction vessel, then long termoperation of the system is impossible. MC alloy on the other handdisplays good initial corrosion resistance to supercritical watercontaining acids such as sulfuric acid, phosphoric acid and hydrofluoricacid. However, because the phase stability of the alloy is not entirelysatisfactory, phase transformation tends to occur at the operatingtemperature, leading to a deterioration in the corrosion resistance.Consequently, if MC alloy is used in a reaction apparatus, then longterm operation of the system is impossible.

Furthermore Inconel 625 and Hastelloy C-276 do not provide adequatecorrosion resistance, with pitting occurring at the contact surfacesbetween the alloy and the supercritical water containing hydrochloricacid. As a result, if either of these materials is employed as thematerial for producing the process reaction vessel in a system used fordetoxifying these types of organic toxic materials, then long termoperation of the system is impossible. MC alloy on the other handdisplays good initial corrosion resistance to supercritical watercontaining hydrochloric acid. However, because the phase stability ofthe alloy is not entirely satisfactory, phase transformation tends tooccur at the operating temperature, leading to a deterioration in thecorrosion resistance. Consequently, if MC alloy is used in a reactionapparatus, then long term operation of the system is impossible.

In addition, when a reaction vessel or piping is produced using Inconel(a registered trademark) 625, Hastelloy (a registered trademark) C-276or Hastelloy (a registered trademark) G-30, then following manufacturinginto a sheet or a pipe to make the process material, this processmaterial must be subjected to further manufacturing process such asrolling or bending to complete the production of the reaction vessel orpiping for the process reaction apparatus. Because a reaction vessel orpiping produced in this manner is prepared by manufacturing process,internal stress or internal distortions remain within the product.Amongst conventional Ni based corrosion resistant alloys, it is knownthat Inconel 625 and Hastelloy C-276 develop stress corrosion crackingin contact with supercritical water containing non-chlorine basedinorganic acids such as sulfuric acid, phosphoric acid and hydrofluoricacid. Consequently, if Inconel 625 or Hastelloy C-276 is used as thematerial for producing the reaction vessel or piping within a system fordetoxifying organic toxic materials, then long term operation of thesystem is impossible. Hastelloy (a registered trademark) G-30 on theother hand displays good initial resistance to stress corrosion crackingwhen exposed to supercritical water containing acids such as sulfuricacid, phosphoric acid and hydrofluoric acid. However, because the phasestability of the alloy is not entirely satisfactory, phasetransformation tends to progress gradually at the operating temperature(400° C. to 650° C.). If a stress field such as that generated by a hightemperature, high pressure supercritical water environment is generatedonce this phase transformation has already progressed significantly,then stress corrosion cracking can occur. Consequently, Hastelloy G-30is not an ideal material for producing a process reaction apparatuscapable of long term operation.

Similarly, if conventional Ni based corrosion resistant alloys such asInconel 625 and Hastelloy C-276 with residual internal stress orinternal distortion are brought into contact with supercritical watercontaining hydrochloric acid or the like, then stress corrosion crackingoccurs. Consequently, if either of these alloys is used for producingthe reaction vessel or piping in a process reaction apparatus fordetoxifying organic toxic materials, then long term operation of thesystem is impossible. Hastelloy (a registered trademark) G-30 on theother hand displays no stress corrosion cracking during initialoperations with supercritical water containing hydrochloric acid.However, because the phase stability of the alloy is not entirelysatisfactory, phase transformation tends to progress gradually at theoperating temperature (400° C. to 650° C.). If a stress field such asthat generated by a high temperature, high pressure supercritical waterenvironment is generated once this phase transformation has alreadyprogressed significantly, then stress corrosion cracking can occur.Consequently, Hastelloy (a registered trademark) G-30 is not an idealmaterial for producing a process reaction apparatus capable of long termoperation.

DISCLOSURE OF INVENTION

The inventors of the present invention conducted intensive researchaimed at producing a Ni based alloy that displays satisfactory corrosionresistance to the types of supercritical water environments containinginorganic acids described above, and also displays excellent phasestability at 400 to 650° C., which would enable operations to becontinued for longer periods. As a result of this research, theydiscovered that a Ni based alloy comprising Cr: from more than 43% to50% or less (all % values refer to % by weight values), Mo: 0.1 to 2%,Mg: 0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0.05 to 0.5%, where necessaryalso comprising either one, or both, of Fe: 0.05 to 1.0% and Si: 0.01 to0.1%, and the remainder as Ni and unavoidable impurities, wherein thequantity of C amongst the unavoidable impurities is restricted to 0.05%or less, displays excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, and alsodisplays excellent phase stability. Moreover, they also discovered thatif this Ni based alloy is used as the material for producing a processreaction apparatus in a system for detoxifying organic toxic materials,then extended operation of the system becomes possible.

One aspect A of the present invention is based on these findings, andprovides:

(A1) a Ni based alloy with excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, comprisingCr: from more than 43% to 50% or less, Mo: 0.1 to 2%, Mg: 0.001 to0.05%, N: 0.001 to 0.04%, Mn: 0.05 to 0.5%, and the remainder as Ni andunavoidable impurities, wherein the quantity of C amongst theunavoidable impurities is restricted to 0.05% or less,

(A2) a Ni based alloy with excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, comprisingCr: from more than 43% to 50% or less, Mo: 0.1 to 2%, Mg: 0.001 to0.05%, N: 0.001 to 0.04%, Mn: 0.05 to 0.5%, further comprising eitherone, or both, of Fe: 0.05 to 1.0% and Si: 0.01 to 0.1%, and theremainder as Ni and unavoidable impurities, wherein the quantity of Camongst the unavoidable impurities is restricted to 0.05% or less, and

(A3) a member for a supercritical water process reaction apparatusformed from a Ni based alloy with a composition according to either oneof (A1) or (A2) above.

As follows is a detailed description of the reasons for restricting thequantity of each element in the compositions of the Ni based alloysaccording to the aforementioned aspect A of the present invention.

Cr:

In a supercritical water environment containing sulfuric acid, Cr isvery effective in promoting corrosion resistance of the aforementionedalloy A. In order to achieve this corrosion resistant effect thequantity of Cr must exceeds 43%, although quantities exceeding 50% makeprocessing of the alloy difficult. Accordingly, the Cr content within aNi based alloy according to this aspect of the present invention is setto a value within the range from more than 43% to 50% or less, and ispreferably from 43.1 to 47%.

Mo:

Mo has a particularly strong effect in improving the corrosionresistance of the alloy A in supercritical water environments containingphosphoric acid. This effect manifests at Mo quantities of at least0.1%, although at quantities exceeding 2% the phase stability tends todeteriorate. Accordingly, the Mo content within a Ni based alloyaccording to this aspect of the present invention is set to a valuewithin the range from 0.1 to 2%, and is preferably from more than 0.1%to less than 0.5%.

N, Mn and Mg:

By jointly incorporating N, Mn and Mg, the phase stability of the alloyA can be improved. In other words, N, Mn and Mg stabilize the Ni-fccmatrix, and help to prevent precipitation of a second phase. However, ifthe N content is less than 0.001%, then the phase stabilizing effectdisappears, whereas if the N content exceeds 0.04%, then nitrides areformed, causing a deterioration in the corrosion resistance relative tosupercritical water environments containing inorganic acids.Accordingly, the N content is set to a value within the range from0.001% to 0.04% (and preferably from 0.005% to 0.03%). Similarly, if theMn content is less than 0.05%, then the phase stabilizing effectdisappears, whereas if the Mn content exceeds 0.5%, the corrosionresistance relative to supercritical water environments containinginorganic acids deteriorates. Accordingly, the Mn content is set to avalue within the range from 0.05% to 0.5% (and preferably from 0.06% to0.1%). Similarly, if the Mg content is less than 0.001%, then the phasestabilizing effect disappears, whereas if the Mg content exceeds 0.05%,the corrosion resistance relative to supercritical water environmentscontaining inorganic acids deteriorates. Accordingly, the Mg content isset to a value within the range from 0.001% to 0.05% (and preferablyfrom 0.002% to 0.04%).

Fe and Si:

Fe and Si have a strengthening effect on the aforementioned alloy A, andare consequently added where improved strength is required. Fe displaysa strength improvement effect at quantities of at least 0.05%, whereasquantities exceeding 1% result in an undesirable deterioration in thecorrosion resistance relative to supercritical water environmentscontaining inorganic acids. Accordingly, the Fe content is set to avalue within the range from 0.05% to 1% (and preferably from 0.1% to0.5%).

Similarly, Si displays a strength improvement effect at quantities of atleast 0.01%, whereas quantities exceeding 0.1% result in an undesirabledeterioration in the corrosion resistance relative to supercriticalwater environments containing inorganic acids. Accordingly, the Sicontent is set to a value within the range from 0.01% to 0.1% (andpreferably from 0.02% to 0.08%).

C:

C is incorporated within the alloy A as an unavoidable impurity, and ifthe quantity is too high, then this C can form carbides with Cr in thevicinity of the grain boundaries, causing a deterioration in thecorrosion resistance. As a result, lower C content values are preferred,and the maximum value for the C content within the unavoidableimpurities is set at 0.05%.

In addition, the inventors of the present invention then conductedfurther intensive research aimed at producing a Ni based alloy thatdisplays satisfactory corrosion resistance to the types of supercriticalwater environments containing inorganic acids described above, and alsodisplays excellent phase stability at 400° C. to 650° C., which wouldenable operations to be continued for even longer periods. As a resultof this research, they discovered that a Ni based alloy comprising Cr:from 29% to less than 42% (all % values refer to % by weight values),Ta: from more than 1% to 3% or less, Mg: 0.001% to 0.05%, N: 0.001% to0.04%, Mn: 0.05% to 0.5%, where necessary also comprising Mo: 0.1% to2%, and/or either one, or both, of Fe: 0.05% to 1.0% and Si: 0.01% to0.1%, and the remainder as Ni and unavoidable impurities, wherein thequantity of C amongst the unavoidable impurities is restricted to 0.05%or less, displays excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, and alsodisplays excellent phase stability. Moreover, they also discovered thatif this Ni based alloy is used as the material for producing a processreaction apparatus in a system for detoxifying organic toxic materials,then even longer operation of the system becomes possible.

Another aspect B of the present invention is based on these findings,and provides:

(B1) a Ni based alloy with excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, comprisingCr: from 29% to less than 42%, Ta: from more than 1% to 3% or less, Mg:0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.05% to 0.5%, and theremainder as Ni and unavoidable impurities, wherein the quantity of Camongst the unavoidable impurities is restricted to 0.05% or less,

(B2) a Ni based alloy with excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, comprisingCr: from 29% to less than 42%, Ta: from more than 1% to 3% or less, Mg:0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.05% to 0.5%, also comprisingMo: 0.1% to 2%, and the remainder as Ni and unavoidable impurities,wherein the quantity of C amongst the unavoidable impurities isrestricted to 0.05% or less,

(B3) a Ni based alloy with excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, comprisingCr: from 29% to less than 42%, Ta: from more than 1% to 3% or less, Mg:0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.05% to 0.5%, furthercomprising either one, or both, of Fe: 0.05% to 1.0% and Si: 0.01% to0.1%, and the remainder as Ni and unavoidable impurities, wherein thequantity of C amongst the unavoidable impurities is restricted to 0.05%or less,

(B4) a Ni based alloy with excellent corrosion resistance relative tosupercritical water environments containing inorganic acids, comprisingCr: from 29% to less than 42%, Ta: from more than 1% to 3% or less, Mg:0.001 to 0.05%, N: 0.001 to 0.04%, Mn: 0.05 to 0.5%, also comprising Mo:0.1 to 2%, further comprising either one, or both, of Fe: 0.05 to 1.0%and Si: 0.01 to 0.1%, and the remainder as Ni and unavoidableimpurities, wherein the quantity of C amongst the unavoidable impuritiesis restricted to 0.05% or less, and

(B5) a member for a supercritical water process reaction apparatusformed from a Ni based alloy with a composition according to any one of(B1), (B2), (B3) and (B4) above.

As follows is a detailed description of the reasons for restricting thequantity of each element in the compositions of the Ni based alloysaccording to this aspect B of the present invention.

Cr and Ta:

In a supercritical water environment containing hydrochloric acid,incorporating both Cr and Ta into the aforementioned Ni based alloy Bcauses a marked improvement in the corrosion resistance. The quantity ofCr must be at least 29%. However, if the Cr content is 42% or more, thenthe combination with Ta causes a deterioration in the phase stability,leading to a reduction in the level of corrosion resistance, andconsequently the Cr content is set to a value within a range from 29% toless than 42%, and preferably from 30% to less than 38%.

Furthermore, the Ni based alloy B must also contain more than 1% of Ta,although if the Ta content exceeds 3%, then the combination with Crcauses a deterioration in the phase stability, leading to an undesirablereduction in the level of corrosion resistance. Accordingly, the Tacontent is set to a value within a range from more than 1% to 3% or less(and preferably from 1.1% to 2.5%).

N and Mn:

By jointly incorporating N and Mn, the phase stability of the Ni basedalloy B can be improved. In other words, N and Mn stabilize the Ni-fccmatrix, and help to prevent precipitation of a second phase. However, ifthe N content is less than 0.001%, then the phase stabilizing effectdisappears, whereas if the N content exceeds 0.04%, then nitrides areformed, causing a deterioration in the corrosion resistance relative tosupercritical water environments containing inorganic acids.Accordingly, the N content is set to a value within the range from0.001% to 0.04% (and preferably from 0.005% to 0.03%). Similarly, if theMn content is less than 0.05%, then the phase stabilizing effectdisappears, whereas if the Mn content exceeds 0.5%, the corrosionresistance relative to supercritical water environments containinginorganic acids deteriorates. Accordingly, the Mn content is set to avalue within the range from 0.05% to 0.5% (and preferably from 0.06% to0.1%).

Mg:

Mg is also a component that improves the phase stability of theaforementioned Ni based alloy B, although if the Mg content is less than0.001%, then the phase stabilizing effect disappears, whereas if the Mgcontent exceeds 0.05%, then the corrosion resistance relative tosupercritical water environments containing inorganic acidsdeteriorates. Accordingly, the Mg content is set to a value within therange from 0.001% to 0.05% (and preferably from 0.002% to 0.04%).

Mo:

Mo has a particularly strong effect in further improving the corrosionresistance of the Ni based alloy B in supercritical water environmentscontaining hydrochloric acid, and may be added where required. Thiseffect manifests at Mo quantities of at least 0.1%, although atquantities exceeding 2% the phase stability tends to deteriorate.Accordingly, the Mo content within the Ni based alloy of this aspect Bis set to a value within the range from 0.1% to 2%, and is preferablyfrom more than 0.1% to less than 0.5%.

Fe and Si:

Fe and Si have a strengthening effect on the aforementioned Ni basedalloy B, and are consequently added where improved strength is required.Fe displays a strength improvement effect at quantities of at least0.05%, whereas quantities exceeding 1% result in an undesirabledeterioration in the corrosion resistance relative to supercriticalwater environments containing inorganic acids. Accordingly, the Fecontent is set to a value within the range from 0.05% to 1% (andpreferably from 0.1% to 0.5%).

Similarly, Si displays a strength improvement effect at quantities of atleast 0.01%, whereas quantities exceeding 0.1% result in an undesirabledeterioration in the corrosion resistance relative to supercriticalwater environments containing inorganic acids. Accordingly, the Sicontent is set to a value within the range from 0.01% to 0.1% (andpreferably from 0.02% to 0.1%).

C:

C is incorporated within the Ni based alloy B as an unavoidableimpurity, and if the quantity is too high, then this C can form carbideswith Cr in the vicinity of the grain boundaries, causing a deteriorationin the corrosion resistance. As a result, lower C content values arepreferred, and the maximum value for the C content within theunavoidable impurities is set at 0.05%.

Furthermore, the inventors of the present invention also conductedintensive research aimed at developing a Ni based alloy which does notdevelop stress corrosion cracking even in supercritical waterenvironments containing inorganic acids, and furthermore also displaysexcellent phase stability even when maintained at an operatingtemperature (400° C. to 650° C.) for extended periods, meaning phasetransformation can be suppressed and a satisfactory level of resistanceto stress corrosion cracking can be ensured even in the above type ofsupercritical water environments containing inorganic acids. Using thisNi based alloy, the inventors then developed members for a supercriticalwater process reaction apparatus capable of extended operation insupercritical water environments containing inorganic acids. The resultsof this research included the following findings:

(Ca) a Ni based alloy comprising Cr: from more than 36% to less than 42%(all % values refer to % by weight values), W: from more than 0.01% toless than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.05% to0.5%, and the remainder as Ni and unavoidable impurities, wherein thequantity of C amongst the unavoidable impurities is restricted to 0.05%or less, displays excellent resistance to stress corrosion cracking insupercritical water environments containing non-chlorine based inorganicacids such as sulfuric acid, phosphoric acid and hydrofluoric acid, andalso displays excellent phase stability, and consequently even whenmaintained at an operating temperature (400° C. to 650° C.) for extendedperiods, phase transformation can be suppressed and stress corrosioncracking can be prevented, and if this Ni based alloy is used as thematerial for the reaction apparatus in a system that uses supercriticalwater for detoxifying organic toxic materials, then even longeroperation of the system becomes possible,

(Cb) in a Ni based alloy with the composition described above in (Ca),if the relative proportion of the aforementioned remainder portion isreduced and Nb: from more than 1.0% to 6% or less is added, then theresistance to stress corrosion cracking can be further improved,

(Cc) in a Ni based alloy with the composition described above in (Ca),if the relative proportion of the aforementioned remainder portion isreduced and either one, or both, of Mo: from 0.01% to less than 0.5% andHf: 0.01% to 0.1% are added, then the resistance to stress corrosioncracking can be further improved, and

(Cd) in a Ni based alloy with the composition described above in (Ca),if the relative proportion of the aforementioned remainder portion isreduced and either one, or both, of Fe: 0.1% to 10% and Si: 0.01% to0.1% are added, then the strength of the alloy can be improved.

Another aspect C of the present invention is based on these researchfindings, and provides:

(C1) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, and the remainder as Ni and unavoidable impurities,wherein the quantity of C amongst the unavoidable impurities isrestricted to 0.05% or less,

(C2) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,and the remainder as Ni and unavoidable impurities, wherein the quantityof C amongst the unavoidable impurities is restricted to 0.05% or less,

(C3) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, further comprising either one, or both, of Mo: from 0.01%to less than 0.5% and Hf: 0.01% to 0.1%, and the remainder as Ni andunavoidable impurities, wherein the quantity of C amongst theunavoidable impurities is restricted to 0.05% or less,

(C4) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, further comprising either one, or both, of Fe: 0.1% to10% and Si: 0.01% to 0.1%, and the remainder as Ni and unavoidableimpurities, wherein the quantity of C amongst the unavoidable impuritiesis restricted to 0.05% or less,

(C5) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,further comprising either one, or both, of Mo: from 0.01% to less than0.5% and Hf: 0.01% to 0.1%, and the remainder as Ni and unavoidableimpurities, wherein the quantity of C amongst the unavoidable impuritiesis restricted to 0.05% or less,

(C6) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,further comprising either one, or both, of Fe: 0.1% to 10% and Si: 0.01%to 0.1%, and the remainder as Ni and unavoidable impurities, wherein thequantity of C amongst the unavoidable impurities is restricted to 0.05%or less,

(C7) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising either one, or both, of Mo: from 0.01% toless than 0.5% and Hf: 0.01% to 0.1%, further comprising either one, orboth, of Fe: 0.1% to 10% and Si: 0.01% to 0.1%, and the remainder as Niand unavoidable impurities, wherein the quantity of C amongst theunavoidable impurities is restricted to 0.05% or less,

(C8) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 36% to less than 42%, W: from more than0.01% to less than 0.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,further comprising either one, or both, of Mo: from 0.01% to less than0.5% and Hf: 0.01% to 0.1%, further comprising either one, or both, ofFe: 0.1% to 10% and Si: 0.01% to 0.1%, and the remainder as Ni andunavoidable impurities, wherein the quantity of C amongst theunavoidable impurities is restricted to 0.05% or less, and

(C9) a member for a supercritical water process reaction apparatusformed from a Ni based alloy with a composition according to any one of(C1), (C2), (C3), (C4), (C5), (C6), (C7) and (C8) above.

As follows is a detailed description of the reasons for restricting thequantity of each element in the compositions of the Ni based alloysaccording to this aspect C of the present invention.

Cr and W:

By incorporating a Cr content exceeding 36% and a W content exceeding0.01% within the Ni based alloy, the resistance to stress corrosioncracking in supercritical water environments containing non-chlorinebased inorganic acids such as sulfuric acid, phosphoric acid andhydrofluoric acid can be improved markedly. However if the Cr content is42% or more, then the combination with W causes a deterioration in theresistance to stress corrosion cracking, and consequently the Cr contentis set to a value within a range from more than 36% to less than 42%,and preferably from more than 38% to 41.5% or less. Similarly, if the Wcontent is 0.5% or more, then the combination with Cr causes anundesirable deterioration in the workability of the alloy. Accordingly,the W content is set to a value within a range from more than 0.01% toless than 0.5%, and preferably from 0.1% to 0.45%.

N, Mn and Mg:

By jointly incorporating N, Mn and Mg, the phase stability of the Nibased alloy C can be improved. In other words, N, Mn and Mg stabilizethe Ni-fcc matrix, and help to prevent precipitation of a second phase.However, if the N content is less than 0.001%, then the phasestabilizing effect disappears, whereas if the N content exceeds 0.04%,then nitrides are formed, causing a deterioration in the corrosionresistance in supercritical water environments. Accordingly, the Ncontent is set to a value within the range from 0.001% to 0.04% (andpreferably from 0.005% to 0.03%). Similarly, if the Mn content is lessthan 0.05%, then the phase stabilizing effect disappears, whereas if theMn content exceeds 0.5%, the resistance to stress corrosion cracking insupercritical water environments containing inorganic acidsdeteriorates. Accordingly, the Mn content is set to a value within therange from 0.05% to 0.5% (and preferably from 0.1% to 0.4%). Similarly,Mg also functions as a component capable of improving the phasestability, although if the Mg content is less than 0.001%, then thephase stabilizing effect disappears, whereas if the Mg content exceeds0.05%, the resistance to stress corrosion cracking in supercriticalwater environments containing inorganic acids deteriorates. Accordingly,the Mg content is set to a value within the range from 0.001% to 0.05%(and preferably from 0.010% to 0.040%).

Nb:

By adding Nb to a Ni based alloy with a Cr content exceeding 36% and a Wcontent exceeding 0.01%, the overall corrosion resistance of the alloyin supercritical water environments containing oxygen but containing nochlorine can be further improved, and accordingly Nb can be added asrequired. The resistance improvement effect manifests at quantitiesexceeding 1.0%, but if the Nb content exceeds 6%, then the phasestability deteriorates. Accordingly, the Nb content in a Ni based alloyof the aspect C is set to a value within a range from more than 1.0% to6% or less, and preferably from 1.1% to less than 3.0%.

Mo and Hf:

By adding Mo and Hf to a Ni based alloy with a Cr content exceeding 36%and a W content exceeding 0.01%, the resistance of the alloy to stresscorrosion cracking in supercritical water environments containing oxygenbut containing no chlorine can be further improved, and accordingly Moand Hf can be added as required. This effect manifests at Mo quantitiesexceeding 0.01%, although at quantities of at least 0.5% the phasestability tends to deteriorate, causing an undesirable deterioration inthe resistance of the alloy to stress corrosion cracking insupercritical water environments containing inorganic acids.Accordingly, the Mo content is set to a value within the range from morethan 0.01% to less than 0.5% (and preferably from more than 0.1% to lessthan 0.5%).

Similarly, Hf displays a resistance improvement effect at quantities ofat least 0.01%, whereas quantities exceeding 0.1% result in anundesirable deterioration in the resistance to stress corrosion crackingin supercritical water environments containing inorganic acids.Accordingly, the Hf content is set to a value within the range from0.01% to 0.1% (and preferably from 0.02% to 0.05%).

Fe and Si:

Fe and Si have a strengthening effect, and are consequently added whereimproved strength is required. Fe displays a strength improvement effectat quantities of at least 0.1%, whereas quantities exceeding 10% resultin an undesirable deterioration in the overall corrosion resistance insupercritical water environments containing inorganic acids.Accordingly, the Fe content is set to a value within the range from 0.1%to 10% (and preferably from 0.5% to 4%).

Similarly, Si displays a strength improvement effect at quantities of atleast 0.01%, whereas quantities exceeding 0.1% result in a deteriorationin the phase stability, causing an undesirable deterioration in theresistance to stress corrosion cracking in supercritical waterenvironments containing inorganic acids. Accordingly, the Si content isset to a value within the range from 0.01% to 0.1% (and preferably from0.02% to 0.05%).

C:

C is incorporated in the alloy as an unavoidable impurity, and if thequantity is too high, then this C can form carbides with Cr in thevicinity of the grain boundaries, causing a general deterioration in theoverall corrosion resistance. As a result, lower C content values arepreferred, and the maximum value for the C content within theunavoidable impurities is set at 0.05%.

In addition, the inventors of the present invention also conductedintensive research aimed at developing a Ni based alloy which does notdevelop stress corrosion cracking even in supercritical waterenvironments containing inorganic acids, and furthermore also displaysexcellent phase stability even when maintained at an operatingtemperature (400° C. to 650° C.) for extended periods, meaning phasetransformation can be suppressed and a satisfactory level of resistanceto stress corrosion cracking can be ensured even in the above type ofsupercritical water environments containing inorganic acids. Using thisNi based alloy, the inventors then developed members for a supercriticalwater process reaction apparatus capable of extended operation undersupercritical water environments containing inorganic acids. The resultsof this research included the following findings:

(Da) a Ni based alloy comprising Cr: from more than 28% to less than 34%(all % values refer to % by weight values), W: from more than 0.1% toless than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.05% to0.5%, and the remainder as Ni and unavoidable impurities, wherein thequantity of C amongst the unavoidable impurities is restricted to 0.05%or less, displays excellent resistance to stress corrosion cracking insupercritical water environments containing inorganic acids, andparticularly supercritical water environments containing chlorine-basedinorganic acids, and also displays excellent phase stability, andconsequently even when maintained at an operating temperature (400° C.to 650° C.) for extended periods, phase transformation can be suppressedand stress corrosion cracking can be prevented, and if this Ni basedalloy is used as the material for the process reaction apparatus in asystem that uses supercritical water for detoxifying organic toxicmaterials, then extended operation of the system becomes possible,

(Db) in a Ni based alloy with the composition described above in (Da),if the relative proportion of the aforementioned remainder portion isreduced and Nb: from more than 1.0% to 6% or less is added, then theresistance to stress corrosion cracking can be further improved,

(Dc) in a Ni based alloy with the composition described above in (Da),if the relative proportion of the aforementioned remainder portion isreduced and either one, or both, of Mo: from 0.01% to less than 0.5% andHf: 0.01% to 0.1% are added, then the resistance to stress corrosioncracking can be further improved, and

(Dd) in a Ni based alloy with the composition described above in (Da),if the relative proportion of the aforementioned remainder portion isreduced and either one, or both, of Fe: 0.1% to 10% and Si: 0.01% to0.1% are added, then the strength of the alloy can be improved.

Another aspect D of the present invention is based on these researchfindings, and provides:

(D1) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, and the remainder as Ni and unavoidable impurities,wherein the quantity of C amongst the unavoidable impurities isrestricted to 0.05% or less,

(D2) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,and the remainder as Ni and unavoidable impurities, wherein the quantityof C amongst the unavoidable impurities is restricted to 0.05% or less,

(D3) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, further comprising either one, or both, of Mo: from 0.01%to less than 0.5% and Hf: 0.01% to 0.1%, and the remainder as Ni andunavoidable impurities, wherein the quantity of C amongst theunavoidable impurities is restricted to 0.05% or less,

(D4) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, further comprising either one, or both, of Fe: 0.1% to10% and Si: 0.01% to 0.1%, and the remainder as Ni and unavoidableimpurities, wherein the quantity of C amongst the unavoidable impuritiesis restricted to 0.05% or less,

(D5) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,further comprising either one, or both, of Mo: from 0.01% to less than0.5% and Hf: 0.01% to 0.1%, and the remainder as Ni and unavoidableimpurities, wherein the quantity of C amongst the unavoidable impuritiesis restricted to 0.05% or less,

(D6) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,further comprising either one, or both, of Fe: 0.1% to 10% and Si: 0.01%to 0.1%, and the remainder as Ni and unavoidable impurities, wherein thequantity of C amongst the unavoidable impurities is restricted to 0.05%or less,

(D7) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising either one, or both, of Mo: from 0.01% toless than 0.5% and Hf: 0.01% to 0.1%, further comprising either one, orboth, of Fe: 0.1% to 10% and Si: 0.01% to 0.1%, and the remainder as Niand unavoidable impurities, wherein the quantity of C amongst theunavoidable impurities is restricted to 0.05% or less,

(D8) a Ni based alloy with excellent resistance to stress corrosioncracking in supercritical water environments containing inorganic acids,comprising Cr: from more than 28% to less than 34%, W: from more than0.1% to less than 1.0%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn:0.05% to 0.5%, also comprising Nb: from more than 1.0% to 6% or less,further comprising either one, or both, of Mo: from 0.01% to less than0.5% and Hf: 0.01% to 0.1%, further comprising either one, or both, ofFe: 0.1% to 10% and Si: 0.01% to 0.1%, and the remainder as Ni andunavoidable impurities, wherein the quantity of C amongst theunavoidable impurities is restricted to 0.05% or less, and

(D9) a member for a supercritical water process reaction apparatusformed from a Ni based alloy with a composition according to any one of(D1), (D2), (D3), (D4), (D5), (D6), (D7) and (D8) above.

As follows is a detailed description of the reasons for restricting thequantity of each element in the compositions of the Ni based alloysaccording to this aspect D of the present invention.

Cr and W:

In a supercritical water environment containing hydrochloric acid, theresistance to stress corrosion cracking can be improved markedly byincorporating both Cr and W into the Ni based alloy of the aspect D. TheCr content must exceed 28%. However if the Cr content is 34% or more,then the combination with W causes a deterioration in the overallcorrosion resistance, and consequently the Cr content is set to a valuewithin a range from more than 28% to less than 34%, and preferably from28.5% to less than 33%.

Similarly, the W content in a Ni based alloy of the aspect D must exceed0.1%. However, if the W content is 1.0% or more then the combinationwith Cr causes a deterioration in the phase stability, resulting in anundesirable deterioration in the resistance to stress corrosioncracking. Accordingly, the W content is set to a value within a rangefrom more than 0.1% to less than 1.0% (and preferably from more than0.1% to 0.5% or less).

N, Mn and Mg

By jointly incorporating N, Mn and Mg, the phase stability of the Nibased alloy D can be improved. In other words, N, Mn and Mg stabilizethe Ni-fcc matrix, and help to prevent precipitation of a second phase.However, if the N content is less than 0.001%, then the phasestabilizing effect disappears, whereas if the N content exceeds 0.04%,then nitrides are formed, causing a deterioration in the corrosionresistance relative to supercritical water environments. Accordingly,the N content is set to a value within the range from 0.001% to 0.04%(and preferably from 0.005% to 0.03%). Similarly, if the Mn content isless than 0.05%, then the phase stabilizing effect disappears, whereasif the Mn content exceeds 0.5%, the resistance to stress corrosioncracking in supercritical water environments containing inorganic acidsdeteriorates. Accordingly, the Mn content is set to a value within therange from 0.05% to 0.5% (and preferably from 0.1% to 0.4%). Similarly,Mg also functions as a component capable of improving the phasestability, although if the Mg content is less than 0.001%, then thephase stabilizing effect disappears, whereas if the Mg content exceeds0.05%, the resistance to stress corrosion cracking in supercriticalwater environments containing inorganic acids deteriorates. Accordingly,the Mg content is set to a value within the range from 0.001% to 0.05%(and preferably from 0.010% to 0.040%).

Nb:

Nb is effective in improving the overall corrosion resistance of thealloy, particularly in supercritical water environments containinghydrochloric acid, and accordingly is added to the alloy as required.The resistance improvement effect manifests at quantities exceeding1.0%, but if the Nb content exceeds 6%, then the phase stabilitydeteriorates. Accordingly, the Nb content in a Ni based alloy of theaspect D is set to a value within a range from more than 1.0% to 6% orless, and preferably from 1.1% to less than 3.0%.

Mo and Hf:

Mo and Hf are effective in improving the resistance to stress corrosioncracking, particularly in supercritical water environments containinghydrochloric acid, and accordingly are added to the alloy as required.This effect manifests at Mo quantities exceeding 0.01%, although atquantities of 0.5% or more the phase stability tends to deteriorate,causing an undesirable deterioration in the resistance of the alloy tostress corrosion cracking in supercritical water environments containinginorganic acids. Accordingly, the Mo content is set to a value withinthe range from more than 0.01% to less than 0.5% (and preferably frommore than 0.1% to less than 0.5%).

Similarly, Hf displays a resistance improvement effect at quantities ofat least 0.01%, whereas quantities exceeding 0.1% result in anundesirable deterioration in the resistance to stress corrosion crackingin supercritical water environments containing inorganic acids.Accordingly, the Hf content is set to a value within the range from0.01% to 0.1% (and preferably from 0.02% to 0.05%).

Fe and Si:

Fe and Si have a strengthening effect, and are consequently added whereimproved strength is required. Fe displays a strength improvement effectat quantities of at least 0.1%, whereas quantities exceeding 10% resultin an undesirable deterioration in the overall corrosion resistance insupercritical water environments containing inorganic acids.Accordingly, the Fe content is set to a value within the range from 0.1%to 10% (and preferably from 0.5% to 4.0%).

Similarly, Si displays a strength improvement effect at quantities of atleast 0.01%, whereas quantities exceeding 0.1% result in an undesirabledeterioration in the phase stability, causing a deterioration in theresistance to stress corrosion cracking in supercritical waterenvironments containing inorganic acids. Accordingly, the Si content isset to a value within the range from 0.01% to 0.1% (and preferably from0.02% to 0.05%).

C:

C is incorporated in the alloy as an unavoidable impurity, and if thequantity is too high, then this C can form carbides with Cr in thevicinity of the grain boundaries, causing a general deterioration in theoverall corrosion resistance. As a result, lower C content values arepreferred, and the maximum value for the C content within theunavoidable impurities is set at 0.05%.

DESCRIPTION OF THE INVENTION

(Aspect A)

Using a raw material with a low C content in each case, the raw materialwas melted and cast in a normal high frequency induction furnace toprepare an ingot of thickness 12 mm. The ingot was then subjected tohomogenizing heat treatment for 10 hours at 1230° C. Subsequently, withthe temperature held within a range from 1000° C. to 1230° C., hotrolling was used to reduce the thickness by 1 mm per repetition, andthis process was repeated until a final thickness of 5 mm was achieved.The sample was then subjected to solution treatment by holding thesample at 1200° C. for 30 minutes followed by water quenching. Thesurface of the sample was then buffed, yielding a Ni based alloy sheetA1 to A21 of the present invention, or a comparative Ni based alloysheet AC1 to AC11, with a composition shown in Table A1 to Table A3. Inaddition, using the compositions shown in Table A3, commerciallyavailable Ni based alloy sheets AU1 to AU3 of thickness 5 mm were alsoprepared.

Each of the Ni based alloy sheets A1 to A21 of the present invention,the comparative Ni based alloy sheets AC1 to AC11, and the conventionalNi based alloy sheets AU1 to AU3 was cut to prepare solution testspecimens of dimensions 10 mm×50 mm. In addition, in order to evaluatethe effect of the phase stability on the corrosion resistance relativeto a supercritical water environment containing inorganic acids, each ofthe Ni based alloy sheets A1 to A21 of the present invention, thecomparative Ni based alloy sheets AC1 to AC11, and the conventional Nibased alloy sheets AU1 to AU3 was subjected to aging treatment byholding the sheet at 550° C. for 1000 hours, and the sheet was then cutto prepare aged test specimens of dimensions 10 mm×50 mm.

Next, a flow type corrosion test apparatus was prepared using aHastelloy C-276 pipe as an autoclave. A test solution is pumped into oneend of the Hastelloy C-276 pipe of this flow type corrosion testapparatus using a high pressure pump, and is discharged from the otherend of the pipe, while the test solution inside the Hastelloy C-276 pipeis maintained at a predetermined flow rate. The test solution is heatedby a heater provided on the Hastelloy C-276 pipe, and the test solutionis able to be maintained at a predetermined temperature. In addition,the test solution discharged from the other end of the Hastelloy C-276pipe of the flow type corrosion test apparatus passes through a pressurereducing valve and is recovered in a reservoir tank.

Using the flow type corrosion test apparatus described above, corrosiontests were conducted using the inorganic acid containing supercriticalwater simulated solutions described below.

(Aa) A test solution was prepared by mixing 0.2 mol/kg of sulfuric acidand 0.2 mol/kg of phosphoric acid into supercritical water with a fluidtemperature of 550° C., a pressure of 40 MPa and a dissolved oxygenlevel of 8 ppm. This solution is an estimation of the supercriticalwater solution generated when VX gas is decomposed and oxidized insupercritical water (and is hereafter referred to as a simulated VX gasdecomposition supercritical water solution). This simulated VX gasdecomposition supercritical water solution was fed into the HastelloyC-276 pipe of the aforementioned flow type corrosion test apparatus, andthe flow rate of the simulated VX gas decomposition supercritical watersolution inside the Hastelloy C-276 pipe was adjusted to 6 g/min, thusforming a supercritical water environment containing inorganic acids.Solution test specimens of the Ni based alloy sheets A1 to A21 of thepresent invention, the comparative Ni based alloy sheets AC1 to AC11,and the conventional Ni based alloy sheets AU1 to AU3 were then eachheld in this supercritical water environment for a period of 100 hours.The reduction in weight of the solution test specimen over the course ofthe test was divided by the surface area of the specimen to determinethe weight loss per unit area for each test specimen. The results areshown in Table A1 through Table A3.

In addition, in order to evaluate the effect of the phase stability onthe corrosion resistance relative to a supercritical water environmentcontaining inorganic acids, aged test specimens of the Ni based alloysheets A1 to A21 of the present invention, the comparative Ni basedalloy sheets AC1 to AC11, and the conventional Ni based alloy sheets AU1to AU3 were each held in the above supercritical water environmentcontaining inorganic acids for a period of 100 hours. The reduction inweight of the test specimen over the course of the test was divided bythe surface area of the aged test specimen to determine the weight lossper unit area for each test specimen. The results are shown in Table A1through Table A3.

(Ab) A test solution was prepared by mixing 0.4 mol/kg of phosphoricacid and 0.1 mol/kg of hydrofluoric acid into supercritical water with afluid temperature of 550° C., a pressure of 40 MPa and a dissolvedoxygen level of 8 ppm. This solution is an estimation of thesupercritical water solution generated when GB (sarin) gas is decomposedand oxidized in supercritical water (and is hereafter referred to as asimulated GB gas decomposition supercritical water solution). Thissimulated GB gas decomposition supercritical water solution was fed intothe Hastelloy C-276 pipe of the aforementioned flow type corrosion testapparatus, and the flow rate of the simulated GB gas decompositionsupercritical water solution inside the Hastelloy C-276 pipe wasadjusted to 6 g/min, thus forming a supercritical water environmentcontaining inorganic acids. Solution test specimens of the Ni basedalloy sheets A1 to A21 of the present invention, the comparative Nibased alloy sheets AC1 to AC11, and the conventional Ni based alloysheets AU1 to AU3 were then each held in this supercritical waterenvironment for a period of 100 hours. The reduction in weight of thesolution test specimen over the course of the test was divided by thesurface area of the specimen to determine the weight loss per unit areafor each test specimen. The results are shown in Table A1 through TableA3.

In addition, in order to evaluate the effect of the phase stability onthe corrosion resistance relative to a supercritical water environmentcontaining inorganic acids, aged test specimens of the Ni based alloysheets A1 to A21 of the present invention, the comparative Ni basedalloy sheets AC1 to AC11, and the conventional Ni based alloy sheets AU1to AU3 were each held in the above supercritical water environmentcontaining inorganic acids for a period of 100 hours. The reduction inweight of the test specimen over the course of the test was divided bythe surface area of the aged test specimen to determine the weight lossper unit area for each test specimen. The results are shown in Table A1through Table A3.

TABLE A1 Corrosion tests Corrosion tests using simulated using simulatedVX gas GB gas decomposition decomposition supercritical supercriticalwater solution water solution weight weight weight weight reductionreduction reduction reduction Composition (% by weight) in solution inaged in solution in aged Ni based Ni and test test test test alloyunavoidable specimen specimen specimen specimen sheet Cr Mo Mg N Mn FeSi C# impurities (mg/cm²) (mg/cm²) (mg/cm²) (mg/cm²) Present A1 44.01.00 0.008 0.021 0.07 — — 0.02 remainder 3 4 5 6 Invention A2 43.1 0.310.006 0.008 0.22 — — 0.02 remainder 7 7 8 8 A3 49.7 0.45 0.007 0.0110.13 — — 0.03 remainder 4 8 3 9 A4 44.2 0.12 0.011 0.021 0.28 — — 0.02remainder 4 6 5 7 A5 43.2 1.96 0.021 0.013 0.10 — — 0.02 remainder 5 7 68 A6 45.6 0.46 0.001 0.014 0.09 — — 0.01 remainder 4 6 2 4 A7 44.0 0.360.049 0.002 0.14 — — 0.02 remainder 5 9 5 9 A8 44.5 0.35 0.022 0.0390.12 — — 0.02 remainder 4 6 6 7 A9 46.5 0.47 0.006 0.022 0.05 — — 0.02remainder 3 5 7 9 A10 45.1 0.49 0.008 0.025 0.49 — — 0.01 remainder 4 65 8 A11 45.6 0.48 0.031 0.018 0.13 0.05 — 0.03 remainder 5 6 6 7 A1243.3 0.47 0.026 0.009 0.24 0.98 — 0.02 remainder 4 7 7 9 A13 44.4 0.480.017 0.022 0.17 — 0.01 0.02 remainder 3 5 6 8 A14 44.1 0.46 0.004 0.0220.11 — 0.09 0.02 remainder 4 6 5 7 C# refers to the C quantityincorporated as an unavoidable impurity

TABLE A2 Corrosion tests Corrosion tests using simulated using simulatedVX gas GB gas decomposition decomposition supercritical supercriticalwater solution water solution weight weight weight weight reductionreduction reduction reduction Composition (% by weight) in solution inaged in solution in aged Ni based Ni and test test test test alloyunavoidable specimen specimen specimen specimen sheet Cr Mo Mg N Mn FeSi C# impurities (mg/cm²) (mg/cm²) (mg/cm²) (mg/cm²) Present A15 43.50.47 0.040 0.034 0.17 — — 0.03 remainder 5 2 5 3 Invention A16 46.8 0.380.026 0.012 0.33 — — 0.02 remainder 3 2 4 3 A17 44.5 0.47 0.009 0.0200.28 0.22 0.05 0.02 remainder 4 3 4 4 A18 46.5 0.47 0.011 0.006 0.260.14 0.06 0.02 remainder 5 3 5 4 A19 45.0 0.35 0.018 0.028 0.23 0.330.04 0.02 remainder 4 3 5 4 A20 43.9 0.49 0.010 0.026 0.11 0.12 0.030.02 remainder 5 4 6 5 A21 44.8 0.48 0.006 0.027 0.39 — — 0.01 remainder4 2 5 4 Comparison AC1 42.6* 0.56 0.041 0.032 0.23 — — 0.02 remainder 1011 13 13 AC2 55.5* 0.55 0.036 0.035 0.26 — — 0.02 remainder 4 12 5 15AC3 44.5 —* 0.044 0.034 0.33 — — 0.02 remainder 7 8 13 15 AC4 45.0 2.3*0.011 0.022 0.24 — — 0.03 remainder 6 15 4 17 AC5 46.0 0.86 —* 0.0120.28 — — 0.02 remainder 5 14 5 16 AC6 45.5 0.65 0.060* 0.015 0.20 — —0.02 remainder 5 13 6 15 AC7 45.2 0.45 0.027 —* 0.08 — — 0.02 remainder3 14 4 15 *indicates a value outside the composition range of thepresent invention C# refers to the C quantity incorporated as anunavoidable impurity

TABLE A3 Corrosion tests Corrosion tests using simulated using simulatedVX gas GB gas decomposition decomposition supercritical supercriticalwater solution water solution weight weight weight weight reductionreduction reduction reduction Composition (% by weight) in solution inaged in solution in aged Ni based Ni and test test test test alloyunavoidable specimen specimen specimen specimen sheet Cr Mo Mg N Mn FeSi C# impurities (mg/cm²) (mg/cm²) (mg/cm²) (mg/cm²) Comparison AC8 44.10.67 0.031 0.045* 0.17 — — 0.02 remainder 14 16 15 18 AC9 46.3 0.450.024 0.019 0.04* — — 0.01 remainder 4 4 6 16 AC10 44.8 0.57 0.021 0.0280.55* — — 0.02 remainder 15 16 17 19 AC11 43.8 0.66 0.044 0.033 0.21 — —0.07* remainder 8 14 9 15 Conventional AU1 21.0 8.4 Co: 0.6 0.2 3.8 Ta +Nb: 3.6 remainder 40 37 57 49 AU2 15.5 16.1 W: 3.7, Co: 0.5 0.5 5.7 — —remainder 54 45 70 66 AU3 44.1 1.0 — 0.2 0.1 — — remainder 6 4 35 25*indicates a value outside the composition range of the presentinvention C# refers to the C quantity incorporated as an unavoidableimpurity

From the results shown in Table A1 to Table A3 it is evident that boththe solution test specimen and the aged test specimen for each of the Nibased alloy sheets A1 to A21 of the present invention displayed asmaller reduction in weight per unit area than either of theconventional Ni based alloy sheets AU1 or AU2, indicating a superiorlevel of corrosion resistance. In addition, compared with theconventional Ni based alloy AU3, the Ni based alloy sheets A1 to A21 ofthe present invention displayed a smaller reduction in weight per unitarea for the aged test specimen. These results confirm the excellentlevel of corrosion resistance provided by the aged test specimens of theNi based alloy sheets A1 to A21 of the present invention. Furthermore,in the case of the comparative Ni based alloys AC1 to AC11, which havecompositions outside the ranges specified by the present invention, itis evident that either the corrosion resistance of the solution testspecimen and/or the corrosion resistance of the aged test specimen isunsatisfactory in each case.

(Aspect B)

Using a raw material with a low C content in each case, the raw materialwas melted and cast in a normal high frequency induction furnace toprepare an ingot of thickness 12 mm. The ingot was then subjected tohomogenizing heat treatment for 10 hours at 1230° C. Subsequently, withthe temperature held within a range from 1000 to 1230° C., hot rollingwas used to reduce the thickness by 1 mm per repetition, and thisprocess was repeated until a final thickness of 5 mm was achieved. Thesample was then subjected to solution treatment by holding the sample at1200° C. for 30 minutes followed by water quenching. The surface of thesample was then buffed, yielding a Ni based alloy sheet B1 to B21 of thepresent invention, or a comparative Ni based alloy sheet BC1 to BC11,with a composition shown in Table B1 to Table B3. In addition, using thecompositions shown in Table B3, commercially available Ni based alloysheets BU1 to BU3 of thickness 5 mm were also prepared.

Each of the Ni based alloy sheets B1 to B21 of the present invention,the comparative Ni based alloy sheets BC1 to BC11, and the conventionalNi based alloy sheets BU1 to BU3 was cut to prepare solution testspecimens of dimensions 10 mm×50 mm. In addition, in order to evaluatethe effect of the phase stability on the corrosion resistance relativeto a supercritical water environment containing inorganic acids, each ofthe Ni based alloy sheets B1 to B21 of the present invention, thecomparative Ni based alloy sheets BC1 to BC11, and the conventional Nibased alloy sheets BU1 to BU3 was subjected to aging treatment byholding the sheet at 550° C. for 1000 hours, and the sheet was then cutto prepare aged test specimens of dimensions 10 mm×50 mm.

Next, a flow type corrosion test apparatus was prepared using aHastelloy C-276 pipe as an autoclave. A test solution is pumped into oneend of the Hastelloy C-276 pipe of this flow type corrosion testapparatus using a high pressure pump, and is discharged from the otherend of the pipe, while the test solution inside the Hastelloy C-276 pipeis maintained at a predetermined flow rate. The test solution is heatedby a heater provided on the Hastelloy C-276 pipe, and the test solutionis able to be maintained at a predetermined temperature. In addition,the test solution discharged from the other end of the Hastelloy C-276pipe of the flow type corrosion test apparatus passes through a pressurereducing valve and is recovered in a reservoir tank.

Using the flow type corrosion test apparatus described above, corrosiontests were conducted using the inorganic acid containing supercriticalwater simulated solution described below. Namely, a test solution wasprepared by mixing 0.05 mol/kg of hydrochloric acid into supercriticalwater with a fluid temperature of 550° C., a pressure of 40 MPa and adissolved oxygen level of 8 ppm. This solution is an estimation of thesupercritical water solution generated when PCBs or dioxin aredecomposed and oxidized in supercritical water (and is hereafterreferred to as a simulated PCB or dioxin decomposition supercriticalwater solution). This simulated PCB or dioxin decompositionsupercritical water solution was fed into the Hastelloy C-276 pipe ofthe aforementioned flow type corrosion test apparatus, and the flow rateof the simulated PCB or dioxin decomposition supercritical watersolution inside the Hastelloy C-276 pipe was adjusted to 6 g/min, thusforming a supercritical water environment containing an inorganic acid.Solution test specimens of the Ni based alloy sheets B1 to B21 of thepresent invention, the comparative Ni based alloy sheets BC1 to BC11,and the conventional Ni based alloy sheets BU1 to BU3 were then eachheld in this supercritical water environment for a period of 100 hours.The surface of each test specimen was then inspected for pitting. Theresults are shown in Table B1 through Table B3.

In addition, in order to evaluate the effect of the phase stability onthe corrosion resistance relative to a supercritical water environmentcontaining this inorganic acid, aged test specimens of the Ni basedalloy sheets B1 to B21 of the present invention, the comparative Nibased alloy sheets BC1 to BC11, and the conventional Ni based alloysheets BU1 to BU3 were each held in the above supercritical waterenvironment containing an inorganic acid for a period of 100 hours. Thesurface of each aged test specimen was then inspected for pitting. Theresults are shown in Table B1 through Table B3.

TABLE B1 Corrosion tests using simulated PCB or dioxin decompositionsupercritical water solution Composition (% by weight) presence ofpresence of Ni and pitting pitting Ni based unavoidable in solution testin aged test alloy sheet Cr Ta Mg N Mn Mo Fe Si C# impurities specimenspecimen Present B1 30.7 2.01 0.016 0.012 0.18 — 0.12 0.021 0.02remainder no no Invention B2 29.3 2.41 0.014 0.008 0.24 — — — 0.02remainder no no B3 41.6 1.01 0.019 0.011 0.14 — — — 0.01 remainder no noB4 37.6 1.11 0.011 0.021 0.29 — — — 0.02 remainder no no B5 33.4 2.960.012 0.013 0.14 — — — 0.02 remainder no no B6 37.6 1.48 0.001 0.0140.19 — — — 0.02 remainder no no B7 34.2 2.36 0.049 0.007 0.16 — — — 0.02remainder no no B8 34.7 2.34 0.016 0.002 0.17 — — — 0.01 remainder no noB9 36.4 1.87 0.023 0.039 0.11 — — — 0.02 remainder no no B10 35.2 1.960.026 0.025 0.05 — — — 0.02 remainder no no B11 35.3 2.38 0.021 0.0180.49 — — — 0.02 remainder no no B12 33.6 1.77 0.018 0.029 0.24 0.11 — —0.02 remainder no no B13 34.8 1.98 0.015 0.020 0.16 1.98 — — 0.02remainder no no B14 34.1 1.76 0.033 0.025 0.11 — 0.5 — 0.02 remainder nono C# refers to the C quantity incorporated as an unavoidable impurity

TABLE B2 Corrosion tests using simulated PCB or dioxin decompositionsupercritical water solution Composition (% by weight) presence ofpresence of Ni and pitting pitting Ni based unavoidable in solution testin aged test alloy sheet Cr Ta Mg N Mn Mo Fe Si C# impurities specimenspecimen Present B15 33.7 1.87 0.031 0.030 0.16 — 0.99 — 0.02 remainderno no Invention B16 34.8 2.34 0.026 0.017 0.38 — — 0.01 0.02 remainderno no B17 34.8 2.17 0.028 0.021 0.18 — — 0.09 0.03 remainder no no B1832.5 2.27 0.030 0.006 0.26 0.21 0.14 — 0.02 remainder no no B19 35.11.75 0.032 0.028 0.23 — 0.33 0.06 0.01 remainder no no B20 34.1 1.690.021 0.013 0.11 0.22 — 0.04 0.02 remainder no no B21 34.7 1.76 0.0230.027 0.39 0.31 0.24 0.03 0.01 remainder no no Comparison BC1 28.5* 1.560.018 0.032 0.24 — — — 0.02 remainder yes yes BC2 43.5* 1.86 0.015 0.0350.21 — — — 0.02 remainder no yes BC3 32.5 —* 0.014 0.034 0.13 — — — 0.02remainder yes yes BC4 35.0 3.30* 0.017 0.022 0.27 — — — 0.01 remainderno yes BC5 36.2 1.83 —* 0.012 0.38 — — — 0.02 remainder no yes BC6 35.41.62 0.055* 0.015 0.22 — — — 0.02 remainder yes yes BC7 35.7 1.45 0.022—* 0.09 — — — 0.02 remainder no yes *indicates a value outside thecomposition range of the present invention C# refers to the C quantityincorporated as an unavoidable impurity

TABLE B3 Corrosion tests using simulated PCB or dioxin decompositionsupercritical water solution Composition (% by weight) presence ofpresence of Ni and pitting pitting Ni based unavoidable in solution testin aged test alloy sheet Cr Ta Mg N Mn Mo Fe Si C# impurities specimenspecimen Comparison BC8 34.8 1.67 0.024 0.045* 0.37 — — — 0.01 remainderyes yes BC9 36.1 1.45 0.016 0.019 0.04* — — — 0.01 remainder no yes BC1034.2 1.57 0.017 0.028 0.55* — — — 0.02 remainder yes yes BC11 35.5 1.210.022 0.018 0.39 — — — 0.07* remainder no yes Conventional BU1 21.0 8.4Co: 0.6 0.2 — 3.8 Ta + Nb: 3.6 remainder yes yes BU2 15.5 16.1 W: 3.7,Co: 0.5 0.5 — 5.7 — — remainder yes yes BU3 44.1 1.0 — 0.2 — 0.1 — —remainder no yes *indicates a value outside the composition range of thepresent invention C# refers to the C quantity incorporated as anunavoidable impurity

From the results shown in Table B1 to Table B3 it is evident that boththe solution test specimen and the aged test specimen for each of the Nibased alloy sheets B1 to B21 of the present invention displayed far lesspitting than either of the conventional Ni based alloy sheets BU1 orBU2, indicating a superior level of corrosion resistance. However, inthe case of the comparative Ni based alloy sheets BC1 to BC11, whichhave compositions outside the ranges specified by the present invention,it is evident that either the corrosion resistance of the solution testspecimen and/or the corrosion resistance of the aged test specimen isunsatisfactory in each case.

(Aspect C)

Raw material was melted and cast in a normal high frequency inductionfurnace to prepare ingots of thickness 12 mm, with the compositionsshown in Table C1 through Table C4. Each ingot was then subjected tohomogenizing heat treatment for 10 hours at 1230° C. Subsequently, withthe temperature held within a range from 1000 to 1230° C., hot rollingwas used to reduce the thickness by 1 mm per repetition, and thisprocess was repeated until a final thickness of 5 mm was achieved. Eachsample was then subjected to solution treatment by holding the sample at1200° C. for 30 minutes followed by water quenching. The surface of eachsample was then polished using emery paper #600, yielding a series of Nibased alloy sheets C1 to C42 of the present invention, a series ofcomparative Ni based alloy sheets CC1 to CC11, and a series ofconventional Ni based alloy sheets CU1 to CU3.

In order to impart internal stress and internal distortion to each ofthe Ni based alloy sheets C1 to C42 of the present invention, each ofthe comparative Ni based alloy sheets CC1 to CC11, and each of theconventional Ni based alloy sheets CU1 to CU3, each alloy sheet wassubjected to cold rolling with a draft of 30%, yielding a sheet ofthickness 3.5 mm in each case. Each of these sheets was then cut toprepare a series of rectangular block type solution test specimens, withdimensions of length 4 mm, width 4 mm and height 3.5 mm.

In addition, the method described below was used to evaluate the effectof the phase stability on the resistance to stress corrosion cracking ina supercritical water environment containing inorganic acids. First,each of the Ni based alloy sheets C1 to C42 of the present invention,the comparative Ni based alloy sheets CC1 to CC11, and the conventionalNi based alloy sheets CU1 to CU3 was subjected to aging treatment byholding the sheet at 450° C. for 10,000 hours. The sheet was thenpolished using emery paper #600, and was subsequently subjected to coldrolling with a draft of 30% to impart internal stress and internaldistortion to the sheet, thereby yielding a sheet of thickness 3.5 mm ineach case. Each of these sheets was then cut to prepare a series ofrectangular block type aged test specimens, with dimensions of length 4mm, width 4 mm and height 3.5 mm.

Next, a flow type corrosion test apparatus was prepared using atitanium/Hastelloy C-276 double layered pipe comprising titanium on theinside and Hastelloy C-276 on the outside as an autoclave. A testsolution is pumped into one end of the titanium/Hastelloy C-276 doublelayered pipe of this flow type corrosion test apparatus using a highpressure pump, and by heating the test solution with a heater providedat the end of the pipe, predetermined corrosion test conditions can beestablished. The test solution is discharged from the other end of thepipe, passes through a pressure reducing valve and is recovered in areservoir tank.

A test solution was prepared by mixing 0.2 mol/kg of sulfuric acid and0.2 mol/kg of phosphoric acid into supercritical water with a fluidtemperature of 500° C., a pressure of 60 MPa and a dissolved oxygenlevel of 800 ppm (achieved by adding hydrogen peroxide). Thissupercritical water containing sulfuric acid and phosphoric acid is anestimation of the supercritical water solution generated when VX gas isdecomposed and oxidized in supercritical water, and hereafter, thissupercritical water solution containing sulfuric acid and phosphoricacid is referred to as a simulated VX gas decomposition solution.

In addition, another test solution was prepared by mixing 0.4 mol/kg ofphosphoric acid and 0.14 mol/kg of hydrofluoric acid into supercriticalwater with a fluid temperature of 500° C., a pressure of 60 MPa and adissolved oxygen level of 800 ppm (achieved by adding hydrogenperoxide). This supercritical water containing phosphoric acid andhydrofluoric acid is an estimation of the supercritical water solutiongenerated when GB (sarin) gas is decomposed and oxidized insupercritical water, and hereafter, this supercritical water solutioncontaining phosphoric acid and hydrofluoric acid is referred to as asimulated GB gas decomposition solution.

The simulated VX gas decomposition solution and the simulated GB gasdecomposition solution were fed into the titanium/Hastelloy C-276 doublelayered pipe of the aforementioned flow type corrosion test apparatus,and the flow rate of the simulated VX gas decomposition solution orsimulated GB gas decomposition solution inside the double layered pipewas adjusted to 6 g/min, thus forming a supercritical water environmentcontaining inorganic acids. Solution test specimens of the Ni basedalloy sheets C1 to C42 of the present invention, the comparative Nibased alloy sheets CC1 to CC11, and the conventional Ni based alloysheets CU1 to CU3 were then each held in this supercritical waterenvironment for a period of 100 hours. The surface of each test specimenwas then inspected for stress corrosion cracking. The results are shownin Table C5 and Table C6.

In addition, in order to evaluate the effect of the phase stability onthe resistance to stress corrosion cracking in a supercritical waterenvironment containing inorganic acids, aged test specimens of the Nibased alloy sheets C1 to C42 of the present invention, the comparativeNi based alloy sheets CC1 to CC11, and the conventional Ni based alloysheets CU1 to CU3 were each held in the above supercritical waterenvironment containing inorganic acids for a period of 100 hours. Thesurface of each aged test specimen was then inspected for stresscorrosion cracking. The results are shown in Table C5 and Table C6.

TABLE C1 Ni based Composition (% by weight) (Remainder: Ni andunavoidable impurities) alloy sheet Cr W Mg N Mn Nb Mo Hf Fe Si C#Present C1 36.1 0.32 0.0145 0.008 0.27 — — — — — 0.02 Invention C2 41.90.45 0.016 0.010 0.13 — — — — — 0.01 C3 39.3 0.02 0.014 0.021 0.29 — — —— — 0.02 C4 38.2 0.48 0.015 0.015 0.25 — — — — — 0.02 C5 40.4 0.48 0.0020.011 0.14 — — — — — 0.02 C6 39.4 0.36 0.038 0.007 0.12 — — — — — 0.02C7 40.3 0.45 0.027 0.001 0.18 — — — — — 0.02 C8 41.4 0.24 0.014 0.0390.14 — — — — — 0.01 C9 38.2 0.36 0.033 0.026 0.06 — — — — — 0.02 C1039.1 0.38 0.024 0.018 0.49 — — — — — 0.02 C11 40.2 0.14 0.012 0.011 0.161.4 — — 0.26 0.024 0.02 C12 40.7 0.27 0.019 0.027 0.20 1.04 — — — — 0.02C13 37.8 0.29 0.017 0.024 0.25 5.96 — — — — 0.02 C14 37.7 0.37 0.0270.031 0.19 3.6 — — — — 0.02 C# refers to the C quantity incorporated asan unavoidable impurity

TABLE C2 Ni based Composition (% by weight) (Remainder: Ni andunavoidable impurities) alloy sheet Cr W Mg N Mn Nb Mo Hf Fe Si C#Present C15 38.3 0.32 0.015 0.007 0.23 4.5 — — — — 0.02 Invention C1641.1 0.37 0.032 0.027 0.14 2.1 0.01 — — — 0.02 C17 37.7 0.37 0.027 0.0310.19 — 0.49 — — — 0.01 C18 38.2 0.96 0.013 0.014 0.15 — 0.15 — — — 0.02C19 39.4 0.48 0.001 0.013 0.18 — 0.23 — — — 0.02 C20 31.2 0.36 0.0480.008 0.17 — 0.34 — — — 0.02 C21 39.8 0.04 0.023 0.014 0.26 2.9 — 0.01 —— 0.02 C22 39.2 0.17 0.029 0.026 0.17 — — 0.09 — — 0.03 C23 38.2 0.360.026 0.025 0.05 — — 0.03 — — 0.02 C24 39.3 0.38 0.020 0.019 0.49 — —0.05 — — 0.02 C25 37.2 0.44 0.012 0.011 0.18 — — 0.07 — — 0.02 C26 39.50.37 0.031 0.007 0.21 — 0.24 0.03 — — 0.02 C27 38.1 0.45 0.034 0.0270.24 — — — 0.12 — 0.02 C28 36.1 0.03 0.023 0.019 0.13 — — — 9.89 — 0.02C# refers to the C quantity incorporated as an unavoidable impurity

TABLE C3 Ni based Composition (% by weight) (Remainder: Ni andunavoidable impurities) alloy sheet Cr W Mg N Mn Nb Mo Hf Fe Si C#Present C29 38.3 0.32 0.015 0.007 0.23 — — — 2.85 — 0.02 Invention C3039.6 0.45 0.017 0.011 0.14 — — — 5.11 — 0.02 C31 37.6 0.11 0.015 0.0200.28 — — — 6.38 — 0.01 C32 39.7 0.18 0.027 0.025 0.26 — — — — 0.01 0.02C33 38.8 0.43 0.024 0.034 0.19 — — — — 0.09 0.02 C34 38.2 0.36 0.0480.008 0.17 — — — — 0.05 0.02 C35 39.6 0.45 0.030 0.030 0.14 — — — 0.270.03 0.02 C36 40.2 0.22 0.044 0.021 0.21 1.88 0.34 0.02 — 0.02 0.01 C3741.3 0.47 0.032 0.028 0.13 2.03 — 0.05 1.27 0.02 0.02 C38 41.9 0.240.019 0.031 0.17 1.63 — — 2.58 — 0.01 C39 40.6 0.18 0.029 0.025 0.121.22 — — — 0.07 0.02 C40 39.6 0.36 0.027 0.020 0.16 1.56 — 0.04 — — 0.02C41 39.1 0.36 0.030 0.024 0.12 — 0.31 — 3.2 — 0.02 C42 39.7 0.67 0.0310.030 0.16 — — 0.05 — 0.02 0.02 C# refers to the C quantity incorporatedas an unavoidable impurity

TABLE C4 Ni based alloy Composition (% by weight) (Remainder: Ni andunavoidable impurities) sheet Cr W Mg N Mn Mo Fe Si C# Comparison CC135.5* 0.36 0.021 0.038 0.24 — — — 0.01 CC2 42.5* 0.45 0.026 0.035 0.26 —— — 0.01 CC3 39.4 —* 0.035 0.031 0.15 — — — 0.02 CC4 42.0 0.60* 0.0190.025 0.29 — — — 0.02 CC5 39.2 0.13 —* 0.017 0.38 — — — 0.02 CC6 39.40.32 0.055* 0.016 0.22 — — — 0.02 CC7 40.7 0.45 0.029 —* 0.08 — — — 0.02CC8 39.8 0.47 0.021 0.046* 0.39 — — — 0.01 CC9 41.1 0.45 0.026 0.0220.04* — — — 0.01 CC10 39.2 0.37 0.019 0.025 0.55* — — — 0.02 CC11 39.20.44 0.022 0.021 0.18 — — — 0.07* Conventional CU1 21.0 — Co: 0.6 0.28.4 3.8 — CU2 15.5 3.7 Co: 0.5 0.5 16.1 5.7 — CU3 28.7 2.6 Co: 1.87 1.15.0 14.6 Cu: 1.8 *indicates a value outside the composition range of thepresent invention C# refers to the C quantity incorporated as anunavoidable impurity

TABLE C5 Corrosion test results using Corrosion test results usingsimulated VX gas simulated GB gas decomposition solution decompositionsolution Presence of Presence of Presence of Presence of stress stressstress stress corrosion corrosion corrosion corrosion cracking incracking in cracking in cracking in Ni based alloy solution aged testsolution aged test sheet test specimen specimen test specimen specimenPresent C1 no no no no Invention C2 no no no no C3 no no no no C4 no nono no C5 no no no no C6 no no no no C7 no no no no C8 no no no no C9 nono no no C10 no no no no C11 no no no no C12 no no no no C13 no no no noC14 no no no no C15 no no no no C16 no no no no C17 no no no no C18 nono no no C19 no no no no C20 no no no no C21 no no no no C22 no no no noC23 no no no no C24 no no no no C25 no no no no C26 no no no no C27 nono no no C28 no no no no

TABLE C6 Corrosion test results Corrosion test results using simulatedVX gas using simulated GB gas decomposition solution decompositionsolution Presence of Presence of Presence of stress stress stresscorrosion corrosion corrosion Presence of cracking cracking cracking instress corrosion Ni based in solution in aged test solution testcracking in aged alloy sheet test specimen specimen specimen testspecimen Remarks Present C29 no no no no — Invention C30 no no no no —C31 no no no no — C32 no no no no — C33 no no no no — C34 no no no no —C35 no no no no — C36 no no no no — C37 no no no no — C38 no no no no —C39 no no no no — C40 no no no no — C41 no no no no — C42 no no no no —Comparison CC1 no yes no yes — CC2 no — no — cracked during cold rollingCC3 no yes no yes — CC4 no — no — cracked during cold rolling CC5 no yesno yes — CC6 no yes no yes — CC7 no yes no yes — CC8 yes yes yes yes —CC9 no yes no yes — CC10 no yes no yes — CC11 no yes no yes —Conventional CU1 yes yes yes yes — CU2 yes yes yes yes — CU3 no yes noyes —

From the results shown in Table C1 to Table C6 it is evident that boththe solution test specimen and the aged test specimen for each of the Nibased alloy sheets C1 to C42 of the present invention displayed none ofthe stress corrosion cracking seen in the conventional Ni based alloysheets CU1 and CU2, indicating a superior level of resistance to stresscorrosion cracking. However, in the case of the comparative Ni basedalloy sheets CC1 to CC11, which have compositions outside the rangesspecified by the present invention, it is evident that stress corrosioncracking developed in either the solution test specimen and/or the agedtest specimen, and there was also a marked increase in overallcorrosion.

(Aspect D)

Raw material was melted and cast in a normal high frequency inductionfurnace to prepare ingots of thickness 12 mm, with the compositionsshown in Table D1 through Table D4. Each ingot was then subjected tohomogenizing heat treatment for 10 hours at 1230° C. Subsequently, withthe temperature held within a range from 1000 to 1230° C., hot rollingwas used to reduce the thickness by 1 mm per repetition, and thisprocess was repeated until a final thickness of 5 mm was achieved. Eachsample was then subjected to solution treatment by holding the sample at1200° C. for 30 minutes followed by water quenching. The surface of eachsample was then buffed, yielding a series of Ni based alloy sheets D1 toD42 of the present invention, a series of comparative Ni based alloysheets DC1 to DC11, and a series of conventional Ni based alloy sheetsDU1 to DU3.

In order to impart internal stress and internal distortion to each ofthe Ni based alloy sheets D1 to D42 of the present invention, each ofthe comparative Ni based alloy sheets DC1 to DC11, and each of theconventional Ni based alloy sheets DU1 to DU3, each alloy sheet wassubjected to cold rolling with a draft of 20%, yielding a sheet ofthickness 4 mm in each case. Each of these sheets was then cut toprepare a series of cube-like solution test specimens, with dimensionsof length 4 mm, width 4 mm and height 4 mm.

In addition, the method described below was used to evaluate the effectof the phase stability on the resistance to stress corrosion cracking ina supercritical water environment containing inorganic acids. First,each of the Ni based alloy sheets D1 to D42 of the present invention,the comparative Ni based alloy sheets DC1 to DC11, and the conventionalNi based alloy sheets DU1 to DU3 was subjected to aging treatment byholding the sheet at 500° C. for 1000 hours. The sheet was thensubjected to cold rolling with a draft of 20% to impart internal stressand internal distortion to the sheet, thereby yielding a sheet ofthickness 4 mm in each case. Each of these sheets was then cut toprepare a series of cube-like aged test specimens, with dimensions oflength 4 mm, width 4 mm and height 4 mm.

Next, a flow type corrosion test apparatus was prepared using atitanium/Hastelloy C-276 double layered pipe comprising titanium on theinside and Hastelloy C-276 on the outside as an autoclave. A testsolution is pumped into one end of the titanium/Hastelloy C-276 doublelayered pipe of this flow type corrosion test apparatus using a highpressure pump, and by heating the test solution with a heater providedat the end of the pipe, predetermined corrosion test conditions can beestablished. The test solution is discharged from the other end of thepipe, passes through a pressure reducing valve and is recovered in areservoir tank.

A test solution was prepared by mixing 0.03 mol/kg of hydrochloric acidinto supercritical water with a fluid temperature of 500° C., a pressureof 60 MPa and a dissolved oxygen level of 800 ppm (achieved by addinghydrogen peroxide).

This supercritical water containing hydrochloric acid is an estimationof the supercritical water solution generated when PCBs or dioxin aredecomposed and oxidized in supercritical water, and hereafter, thissupercritical water solution containing hydrochloric acid is referred toas a simulated PCB or dioxin decomposition solution.

This simulated PCB or dioxin decomposition solution was fed into thetitanium/Hastelloy C-276 double layered pipe of the aforementioned flowtype corrosion test apparatus, and the flow rate of the simulated PCB ordioxin decomposition solution inside the double layered pipe wasadjusted to 6 g/min, thus forming a supercritical water environmentcontaining an inorganic acid. Solution test specimens of the Ni basedalloy sheets D1 to D42 of the present invention, the comparative Nibased alloy sheets DC1 to DC11, and the conventional Ni based alloysheets DU1 to DU3 were then each held in this supercritical waterenvironment for a period of 100 hours. The surface of each test specimenwas then inspected for stress corrosion cracking. The results are shownin Table D1 through Table D4.

In addition, in order to evaluate the effect of the phase stability onthe resistance to stress corrosion cracking in a supercritical waterenvironment containing inorganic acids, aged test specimens of the Nibased alloy sheets D1 to D42 of the present invention, the comparativeNi based alloy sheets DC1 to DC11, and the conventional Ni based alloysheets DU1 to DU3 were each held in the above supercritical waterenvironment containing an inorganic acid for a period of 100 hours. Thesurface of each aged test specimen was then inspected for stresscorrosion cracking. The results are shown in Table D1 through Table D4.

TABLE D1 Corrosion test results using simulated PCB or dioxindecomposition solution presence of presence of stress stress corrosioncorrosion cracking in cracking in Ni based Composition (% by weight)(Remainder: Ni and unavoidable impurities) solution aged test alloysheet Cr W Mg N Mn Nb Mo Hf Fe Si C# test specimen specimen Present D128.3 0.32 0.015 0.007 0.23 — — — — — 0.02 no no Invention D2 33.6 0.450.017 0.011 0.14 — — — — — 0.02 no no D3 31.6 0.11 0.015 0.020 0.28 — —— — — 0.01 no no D4 32.2 0.96 0.013 0.014 0.15 — — — — — 0.02 no no D530.4 0.48 0.001 0.013 0.18 — — — — — 0.02 no no D6 31.2 0.36 0.048 0.0080.17 — — — — — 0.02 no no D7 30.7 0.55 0.017 0.001 0.18 — — — — — 0.02no no D8 32.4 0.44 0.024 0.038 0.12 — — — — — 0.01 no no D9 33.2 0.360.026 0.025 0.05 — — — — — 0.02 no no D10 29.3 0.38 0.020 0.019 0.49 — —— — — 0.02 no no D11 30.2 0.44 0.012 0.011 0.18 1.3 — — 0.15 0.021 0.02no no D12 32.8 0.28 0.016 0.021 0.15 5.97 — — — — 0.02 no no D13 31.10.36 0.030 0.024 0.12 2.5 — — — — 0.02 no no D14 33.7 0.67 0.031 0.0300.16 3.6 — — — — 0.02 no no C# refers to the C quantity incorporated asan unavoidable impurity

TABLE D2 Corrosion test results using simulated PCB or dioxindecomposition solution presence of presence of stress stress corrosioncorrosion cracking in cracking in Ni based Composition (% by weight)(Remainder: Ni and unavoidable impurities) solution test aged test alloysheet Cr W Mg N Mn Nb Mo Hf Fe Si C# specimen specimen Present D15 28.30.32 0.015 0.007 0.23 4.5 — — — — 0.02 no no Invention D16 31.1 0.360.030 0.024 0.12 2.1 0.02 — — — 0.02 no no D17 33.7 0.67 0.031 0.0300.16 — 0.48 — — — 0.01 no no D18 32.2 0.96 0.013 0.014 0.15 — 0.15 — — —0.02 no no D19 30.4 0.48 0.001 0.013 0.18 — 0.23 — — — 0.02 no no D2031.2 0.36 0.048 0.008 0.17 — 0.34 — — — 0.02 no no D21 34.8 0.34 0.0260.017 0.38 2.9 — 0.01 — — 0.02 no no D22 34.8 0.17 0.028 0.021 0.18 — —0.09 — — 0.03 no no D23 33.2 0.36 0.026 0.025 0.05 — — 0.03 — — 0.02 nono D24 29.3 0.38 0.020 0.019 0.49 — — 0.05 — — 0.02 no no D25 30.2 0.440.012 0.011 0.18 — — 0.07 — — 0.02 no no D26 32.5 0.27 0.030 0.006 0.26— 0.21 0.02 — — 0.02 no no D27 31.1 0.45 0.032 0.029 0.22 — — — 0.14 —0.02 no no D28 30.1 0.49 0.021 0.013 0.11 — — — 9.88 — 0.02 no no C#refers to the C quantity incorporated as an unavoidable impurity

TABLE D3 Corrosion test results using simulated PCB or dioxindecomposition solution presence of presence of stress stress corrosioncorrosion cracking in cracking in Ni based Composition (% by weight)(Remainder: Ni and unavoidable impurities) solution aged test alloysheet Cr W Mg N Mn Nb Mo Hf Fe Si C# test specimen specimen Present D2928.3 0.32 0.015 0.007 0.23 — — — 2.85 — 0.02 no no Invention D30 33.60.45 0.017 0.011 0.14 — — — 5.11 — 0.02 no no D31 31.6 0.11 0.015 0.0200.28 — — — 6.38 — 0.01 no no D32 32.2 0.96 0.013 0.014 0.15 — — — — 0.010.02 no no D33 30.4 0.48 0.001 0.013 0.18 — — — — 0.09 0.02 no no D3431.2 0.36 0.048 0.008 0.17 — — — — 0.05 0.02 no no D35 29.6 0.45 0.0310.031 0.16 — — — 0.26 0.02 0.02 no no D36 30.2 0.32 0.042 0.025 0.201.88 0.33 0.02 — 0.03 0.01 no no D37 31.3 0.47 0.030 0.038 0.14 2.03 —0.04 1.22 0.02 0.02 no no D38 32.9 0.22 0.029 0.033 0.13 1.63 — — 0.58 —0.01 no no D39 30.6 0.18 0.028 0.026 0.11 1.22 — — — 0.08 0.02 no no D4029.6 0.35 0.022 0.022 0.14 1.56 — 0.04 — — 0.02 no no D41 31.1 0.360.030 0.024 0.12 — 0.031 — 3.2 — 0.02 no no D42 33.7 0.67 0.031 0.0300.16 — — 0.05 — 0.02 0.02 no no C# refers to the C quantity incorporatedas an unavoidable impurity

TABLE D4 Corrosion test results using simulated PCB or dioxindecomposition solution presence of presence of stress stress corrosioncorrosion Ni based Composition (% by weight) cracking in cracking inalloy (Remainder: Ni and unavoidable impurities) solution aged testsheet Cr W Mg N Mn Mo Fe Si C# test specimen specimen Remarks ComparisonDC1 27.5* 0.56 0.019 0.034 0.25 — — — 0.02 yes yes — DC2 34.5* 0.850.016 0.031 0.22 — — — 0.02 no no overall corrosion DC3 32.4 —* 0.0150.032 0.16 — — — 0.01 yes yes — DC4 33.0 1.25* 0.018 0.022 0.28 — — —0.02 no yes — DC5 31.2 0.13 —* 0.012 0.39 — — — 0.02 no yes — DC6 32.40.62 0.055* 0.015 0.21 — — — 0.02 yes yes — DC7 32.7 0.55 0.017 —* 0.18— — — 0.02 no yes — DC8 29.8 0.67 0.025 0.046* 0.38 — — — 0.01 yes yes —DC9 31.1 0.45 0.016 0.019 0.04* — — — 0.01 no yes — DC10 33.2 0.57 0.0170.029 0.55* — — — 0.02 yes yes — DC11 30.2 0.44 0.012 0.011 0.18 — — —0.07* no yes — Conventional DU1 21.0 — Co: 0.6 0.2 8.4 3.8 — yes yes —DU2 15.5 3.7 Co: 0.5 0.5 16.1 5.7 — yes yes — DU3 28.7 2.6 Co: 1.87 1.15.0 14.6 Cu: 1.8 no yes — *indicates a value outside the compositionrange of the present invention C# refers to the C quantity incorporatedas an unavoidable impurity

From the results shown in Table D1 to Table D4 it is evident that boththe solution test specimen and the aged test specimen for each of the Nibased alloy sheets D1 to D42 of the present invention displayed none ofthe stress corrosion cracking seen in the conventional Ni based alloysheets DU1 and DU2, indicating a superior level of resistance to stresscorrosion cracking. However, in the case of the comparative Ni basedalloy sheets DC1 to DC11, which have compositions outside the rangesspecified by the present invention, it is evident that either stresscorrosion cracking developed in the solution test specimen and/or theaged test specimen, or there was a marked increase in overall corrosion.

INDUSTRIAL APPLICABILITY

As described above, a Ni based alloy of the aspect A of the presentinvention displays excellent corrosion resistance in supercritical waterenvironments containing sulfuric acid, phosphoric acid and hydrofluoricacid, and can be used in such environments for extended periods, meaningthe alloy has excellent industrial potential in areas such as thedetoxification of chemical weapons and the like.

A Ni based alloy of this aspect A is most effective when used insupercritical water environments containing sulfuric acid, phosphoricacid and hydrofluoric acid, although potential uses of the alloy are notrestricted to this type of environment, and the alloy can also be usedin supercritical water environments containing hydrochloric acid ornitric acid, supercritical water environments containing chloride saltssuch as sodium chloride, magnesium chloride and calcium chloride, orsupercritical water environments containing ammonia. Accordingly, the Nibased alloy can also be used as the material for supercritical waterdevices used for treating space related waste products, atomic wasteproducts, power production waste products, as well as general industrialwaste.

Furthermore, if a Ni based alloy of this aspect A is used in theproduction of the process reaction vessel in a treatment system, thenthe outside of the vessel could also be formed from a strong materialsuch as stainless steel or the like, and the Ni based alloy then used toclad or line the interior surface of the stainless steel vessel.

Furthermore, a Ni based alloy of the aspect B of the present inventiondisplays excellent corrosion resistance in supercritical waterenvironments containing hydrochloric acid, and can be used in suchenvironments for extended periods, meaning the alloy has excellentenvironmental and industrial potential in areas such as thedetoxification of PCBs and dioxin and the like.

A Ni based alloy of this aspect B is most effective when used insupercritical water environments containing hydrochloric acid, althoughpotential uses of the alloy are not restricted to this type ofenvironment, and the alloy can also be used in supercritical waterenvironments containing sulfuric acid, phosphoric acid, hydrofluoricacid or nitric acid, supercritical water environments containingchloride salts such as sodium chloride, magnesium chloride and calciumchloride, or supercritical water environments containing ammonia.Accordingly, the Ni based alloy can also be used as the material forsupercritical water devices used for treating space related wasteproducts, atomic waste products, power production waste products, aswell as general industrial waste.

Furthermore, if a Ni based alloy of this aspect B is used in theproduction of the process reaction vessel in a treatment system, thenthe outside of the vessel could also be formed from a strong materialsuch as stainless steel or the like, and the Ni based alloy then used toclad or line the interior surface of the stainless steel vessel.

In addition, a Ni based alloy of the aspect C of the present inventiondisplays excellent resistance to stress corrosion cracking insupercritical water environments containing either sulfuric acid andphosphoric acid, or phosphoric acid and hydrofluoric acid, and can beused in such environments for extended periods, meaning the alloy hasexcellent environmental and industrial potential in areas such as thedetoxification of VX gas and GB gas and the like.

A Ni based alloy of this aspect C is most effective when used insupercritical water environments containing non-chlorine based inorganicacids such as sulfuric acid, phosphoric acid and hydrofluoric acid,although potential uses of the alloy are not restricted to this type ofenvironment, and the alloy can also be used in supercritical waterenvironments containing hydrochloric acid or nitric acid, supercriticalwater environments containing chloride salts such as sodium chloride,magnesium chloride and calcium chloride, or supercritical waterenvironments containing ammonia. Accordingly, the Ni based alloy canalso be used as the material for supercritical water devices used fortreating space related waste products, atomic waste products, powerproduction waste products, as well as general industrial waste.

Furthermore, if a Ni based alloy of this aspect C is used in theproduction of the reaction chamber in a treatment system, then theoutside of the chamber could also be formed from a strong material suchas stainless steel or the like, and the Ni based alloy then used to clador line the interior surface of the stainless steel chamber.

Furthermore, a Ni based alloy of the aspect D of the present inventiondisplays excellent resistance to stress corrosion cracking insupercritical water environments containing hydrochloric acid, and canbe used in such environments for extended periods, meaning the alloy hasexcellent environmental and industrial potential in areas such as thedetoxification of PCBs and dioxin and the like.

A Ni based alloy of this aspect D is most effective when used insupercritical water environments containing hydrochloric acid, althoughpotential uses of the alloy are not restricted to this type ofenvironment, and the alloy can also be used in supercritical waterenvironments containing sulfuric acid, phosphoric acid, hydrofluoricacid or nitric acid, supercritical water environments containingchloride salts such as sodium chloride, magnesium chloride and calciumchloride, or supercritical water environments containing ammonia.Accordingly, the Ni based alloy can also be used as the material forsupercritical water devices used for treating space related wasteproducts, atomic waste products, power production waste products, aswell as general industrial waste.

Furthermore, if a Ni based alloy of this aspect D is used in theproduction of the reaction chamber in a treatment system, then theoutside of the chamber could also be formed from a strong material suchas stainless steel or the like, and the Ni based alloy then used to clador line the interior surface of the stainless steel chamber.

1. A Ni based alloy with excellent corrosion resistance relative tosupercritical water environments containing inorganic acids consistingof in weight basis: Cr: from more than 43% to 50% or less, Mo: 0.1% to2%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.05% to 0.5%, at leastone of Fe: 0.05% to 1.0% of and Si: 0.01% to 0.1%, and a remainder as Niand unavoidable impurities, wherein a quantity of C amongst saidunavoidable impurities is restricted to 0.05% or less, and the Ni basedalloy consists essentially of a stabilized Ni-FCC matrix.
 2. A memberfor a supercritical water process reaction apparatus, wherein saidmember comprises a Ni based alloy according to claim
 1. 3. A system fordetoxifying organic toxic materials comprising a member for asupercritical water process reaction apparatus, wherein said membercomprises a Ni based alloy consisting of in weight basis: Cr: from morethan 43% to 50% or less, Mo: 0.1% to 2%, Mg: 0.001% to 0.05%, N: 0.001%to 0.04%, Mn: 0.05% to 0.5%, at least one of Fe: 0.05% to 1.0% of andSi: 0.01% to 0.1%, and a remainder as Ni and unavoidable impurities,wherein a quantity of C amongst said unavoidable impurities isrestricted to 0.05% or less, and the Ni based alloy consists essentiallyof a stabilized Ni-FCC matrix.